Electrical connector

ABSTRACT

A device (1) for forming an electrical connection at the end of a bundle of wires (2) comprises an electrically insulating, preferably heat-shrinkable, sleeve (3), a metallic connecting element (4) located within the sleeve, and a quantity of solder (8) for forming a permanent electrical connection between the conductors. The connecting element (4) has a tapering internal surface which has a screw thread so that a temporary electrical connection can be formed by screwing the bundle of wires into the connecting element. Preferably the connecting element is formed by winding a wire, e.g. hard tempered copper wire, into a frusto-conical form. Splices in wire bundles may be made by means of a device in which the connecting element has a pair of internally threaded portions into which different cable bundles can be screwed.

This invention relates to electrical connectors, and especially toconnectors for forming solder joints between conductors in such articlesas automotive harnesses and the like.

Electrical harnesses, for example as manufactured in the automotiveindustry, are often quite complex. In some instances they aremanufactured by forming two or more sub-assemblies of wires, terminals,connectors and any other components, and then forming electricalconnection(s) between the sub-assemblies. In such a case the assembly ofthe harness my be controlled by computer permitting, with the aid of amonitor, the assembly operator to see schematically the lay up and tocheck correct build-up of the assembly at each stage of the harnessmanufacture. In order to enable this control process to operate the endsof the conductors of the sub-assemblies are connected, e.g. by means ofspring contacts, and an electrical current or signal is passed throughthe assembly in order to obtain verification that the harness iscorrect. It is only after such verification is obtained that the clipsare removed and a permanent electrical connection is formed.

According to the invention, there is provided a device for forming anelectrical connection at the end of a bundle of elongate electricalconductors, which comprises an electrically insulating sleeve, ametallic connecting element located within the sleeve, and a quantity ofsolder for forming a permanent electrical connection between theconductors, the connecting element having a tapering internal surfacewhich has a screw thread, so that a temporary electrical connection canbe formed by screwing the bundle of conductors into the connectingelement.

Preferably the device includes an element for holding the bundle beforeor while the permanent electrical connection is formed. For example theelement may resist withdrawal of the bundle so that the connection willbe able to withstand normal handling of the harness during assemblywithout the connection inadvertently becoming loose or breaking, but canbe removed if desired, for example in order to replace one or moresub-assemblies. Such an element may, for example, comprise a ringlocated inside the sleeve which is provided with one or more teeth orgripping edges for engaging insulation of the conductors forming thebundle. The teeth or gripping members preferably have substantially thesame axial inclination as has the screw thread of the connectingelement, so that the bundle can be inserted into the sleeve by rotatingthe bundle within the sleeve and applying a forward pressure, but thatremoval of the sleeve from the insulated conductors by pulling and/orunscrewing is resisted. Alternatively, the element may be provided inorder to hold the bundle during or immediately before recovery of thesleeve. For example, a fusible or infusible (cross-linked) polymericring, preferably a heat-shrinkable polymeric ring may be provided in thesleeve. Such a ring may be made to melt or recover before recovery ofthe sleeve if its melting or recovery point is lower than that of therecoverable sleeve recovery of the ring in this way can be used toreinforce the grip on the bundle and to eliminate or reduce the risk ofpiercing of the sleeve wall by the conductor strands. Such an elementmay, for example have a melting or softening point in the range of from60° to 100° C. Examples of materials from which the polymeric ring maybe formed include ionomers, e.g. Surlyn, or from polyamides, e.g. nylon6, 66, 11 or 12. After the installed device has cooled, the element willassist in maintaining mechanical rigidity of the assembly.

The device according to the invention has the advantage that theconductors can be electrically joined to form a temporary joint which isdisconnectable but is able to have a high degree of dependability, inorder, for example to test the connected conductors, and can then bepermanently joined with no further manipulation of the joint but simplyby heating the sleeve in order to melt the solder. In addition, thetapering interior of the connecting element enables bundles formed froma range of conductor sizes to be handled by the device.

In the broadest aspect of the invention the device includes a connectingelement having a single tapering internal surface so that a stub splicecan be formed between a bundle of conductors inserted into one end ofthe sleeve, the other end of the sleeve for example being closed.However, it is possible for devices according to the invention toinclude connecting elements having more than one tapering internalsurface so that, for example an in-line splice may be formed between apair of bundles of conductors. Thus, according to another aspect, theinvention provides a device for forming a splice between a pair ofbundles of elongate electrical conductors, which comprises anelectrically insulating sleeve, a metallic connecting element locatedwithin the sleeve and a quantity of solder for forming a permanentelectrical connection between the conductors of the bundles, theconnecting element having two end portions each of which has a taperinginternal surface and at least one of which has a screw thread so that atemporary electrical connection can be formed by inserting one of thebundles of conductors into each end portion of the connecting element.

Where the end portions of the connecting element are rotatable withrespect to each other it is often desirable to form the sleeve in twoparts, each part being located on one of the end portions of theconnecting element so that the connecting element end portions can berotated by twisting the part of the sleeve it is located in.

Usually the sleeve will be dimensionally recoverable, and especiallydimensionally heat-recoverable, that is to say the article has adimensional configuration that may be made substantially to change whensubjected to heat treatment.

Usually these articles recover, on heating, towards an original shapefrom which they hake previously been deformed but the term"heat-recoverable", as used herein, also includes an article which, onheating, adopts a new configuration, even if it has not been previouslydeformed.

In their most common form, such articles comprise a heat-shrinkablesleeve made from a polymeric material exhibiting the property of elasticor plastic memory as described, for example, in U.S. Pat. Nos.2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example,U.S. Pat. Nos. 2,027,962, the original dimensionally heat-stable formmay be a transient form in a continuous process in which, for example,an extruded tube is expanded, whilst hot, to a dimensionallyheat-unstable form but, in other applications, a preformed dimensionallyheat-stable article is deformed to a dimensionally heat-unstable form ina separate state.

In the production of heat-recoverable articles, the polymeric materialmay be cross-linked at any stage in the production of the article thatwill enhance the desired dimensional recoverability. One manner ofproducing a heat-recoverable article comprises shaping the polymericsmaterial into the desired heat-stable form, subsequently cross-linkingthe polymeric material, heating the article to a temperature above thecrystalline melting point or, for amorphous materials the softeningpoint, as the case may be, of the polymer, deforming the article andcooling the article whilst in the deformed state so that the deformedstate of the article is retained. In use, since the deformed state ofthe article is heat-unstable, application of heat will cause the articleto assume its original heat-stable shape.

Any material to which the property of dimensional recoverability may beimparted may be used to form the sleeve. Preferred materials includelow, medium or high density polyethylene, ethylene copolymers, e.g. withalpha olefins such as 1-butene or 1-hexene, or vinyl acetate, polyamidesor fluorpolymers, e.g. Polytetrafluoroethylene, vinylidine fluoride orethylene-tetrafluoroethylene copolymer.

The fact that the ends of the conductors are enclosed in the connectionelement will also reduce the risk of any strands of the conductorspiercing the sleeve during recovery thereof. Also, the conductingelement can act as a heat-sink thereby preventing overheating of thedevice during recovery.

At least in the broadest aspect of the invention the connecting elementmy generally have any form although it is preferred for it to be formedby coiling a piece of wire into a tapering coil so that the windingsform the screw thread. Preferably the internal surface of the connectingelement is at least partly conical, for example it may be conical orfrusto-conical. If the connecting element is formed from a wire, it cangrip the bundle of conductors introduced therein due to the resilienceof the wire and the fact that it will be enlarged radially to someextent by the introduction of the bundle. However, in one advantageousform of device it has been radially expanded from its relaxed stateduring manufacture of the device and to be retained in its expandedstate so that it will radially contract, or attempt radially tocontract, when the permanent connection is formed. Thus, for example,the spring may be held out against its resilient recovery forces by thesleeve or by the solder, so that softening of the sleeve or melting ofthe solder will allow the spring to recover. For example, a boss may beformed on the internal surface of the sleeve or on the internal surfaceof the solder which will disappear when the device is heated. The degreeof expansion need not be great, for example it may be not more than 5%or even not more than 2%, since it may be desirable that the coilremains in contact with the solder element when the device is heated.

The wire may be formed with a circular cross-section, although it ispreferred for the wire to have a relatively sharp ridge along itslength, e.g. formed by cold drawing or cold rolling, which, when thewire has been coiled, is directed toward the interior of the coil inorder to form the screw thread. In particular it is advantageous for thewire to be formed with a polygonal, and especially a square,cross-section. The wire may be formed from any appropriate metal ormetal alloy, but preferably is formed from copper, and especially fromcopper having substantially the same purity as that conventionallyemployed for electrical conductors.

Other configurations of connecting element may, however, be employed.For example it may be formed from a solid block of metal that has beentapped with a screw thread. In the case of the connecting element usedfor the splice, it may be convenient, although it is not essential, forboth end portions to be formed in the same way. For example, the entireconnecting element may be formed from a single piece of wire which hasbeen wrapped so as to form a tapering internal profile at each end, itmay be formed from a wire and a solid block that has been tapped with ascrew thread, or it may be formed from two solid blocks of metal.Alternatively, connecting elements in which one end does not have ascrew thread could be employed, in which the bundle of wires is simplypushed into the connecting element. Where the connecting element isprovided with a screw thread at each end, the screw threads may bothhave the same handedness, or one may be right-handed while the other isleft-handed. Since it is not normally necessary to twist the sleeveabout the conductors by more than one quarter to one half a revolutionin order to form a temporary connection the choice of thread sense doesnot cause any particular problem. It is, however, possible for the endportions of the connecting element to be rotatable with respect to eachother. For example, end portions formed from a wire may both besupported on a small cylindrical connecting element by wrapping part ofthe wire into a circumferential groove in the connecting element.

As mentioned above, the device includes a quantity of solder, i.e. aquantity of soft solder as distinct from brazing material, for forming apermanent solder connection. The solder may, for example, simply be inthe form of an Sn₆₃ Pb₃₇ eutectic composition which will melt as thedevice is heated and the sleeve recovers, or more than one soldercomposition having differing melting points may be employed, asdescribed in International Application No. WO88/09068. In this form ofdevice, melting of the higher melting point component, e.g. Sn₉₆.5 Ag₃.5eutectic will provide a visual indication that the device has beenheated sufficiently to melt the lower melting point composition and toform a satisfactory solder joint. If desired the lower melting pointsolder may be a non-eutectic composition and, for example as describedin International Application No. PCT/GB90/00234, the higher and lowermelting point solder compositions may together form a eutecticcomposition. For example, a non-eutectic Sn₆₀ Pb₄₀ lower melting pointcomponent may be employed with a higher melting point component formedfrom pure tin in relative amounts that an Sn₆₃ Pb₃₇ eutectic is formed.The disclosures of these two patent applications are incorporated hereinby reference. An advantage of employing a two component solder, andespecially a tin, Sn₆₀ Pb₄₀ combination is that it reduces thepossibility of "wicking" that is to say, travel of the solder along theconductors and away from the joint area due to capillary action by thestranded conductors, which can be caused by prolonged heating of thedevice.

The solder may be positioned anywhere where it will be able to flow intothe connecting element to form a solder joint. The solder may beemployed in the form of a ring or in any other form for example a ball,and may be disposed symetrically about the sleeve axis or offset fromit. The solder element may, for instance, be located at the smallerdiameter end of the connecting element in which case it may be in theform of a ball or plug, or it may be located in the region of a largediameter end of the connecting element, for example in the form of aring. Preferably the solder is in the from of an element that surroundsthe connecting element, especially where the connecting element is inthe form of a coil so that the fused solder can flow through thewindings of the coil to the interior thereof. More than one quantity ofsolder may be employed, for example where the connecting element hasmore than one tapering internal surface for forming a splice.

According to another aspect, the invention provides a method of formingan electrical harness from a plurality of insulated electrical wires,which includes:

(a) gathering a number of the insulated wires together to form a bundleat least at the end of the wires;

(b) inserting the bundle into a device as described above by means of ascrewing action in order to form a temporary electrical connection;

(c) applying electrical signals to the harness so formed in order toascertain information about it; and

(d) heating the sleeve to form a permanent solder connection between thewires.

The device may be heated by means of a hot air gun or infrared lamp ascommonly used to recover solder connector devices, or the device may beheated by induction heating methods.

Two forms of device according to the invention will now be described byway of example with reference to the accompanying drawings in which:

FIG. 1 is a sectional elevation along the axis of a device according tothe present invention;

FIG. 2 is a cross-section of the wire employed to form the coil of thedevice;

FIG. 3 is a sectional elevation of the device shown in FIG. 1 with abundle of wires inserted therein;

FIG. 4 is a sectional elevation of the completed joint;

FIG. 5 is a sectional elevation along the axis of a second form ofdevice;

FIGS. 6 and 7 are sectional elevations along the axis of connectorssuitable for forming a splice; and

FIGS. 8 and 9 are elevations of two further forms of connections elementthat can be employed in the device of FIG. 7.

Referring to the accompanying drawings a device 1 for forming aconnection between a number of electrically insulated wires 2 comprisesa dimensionally heat-recoverable sleeve 3 formed from crosslinked andexpanded polyvinylidine fluoride, and a connecting element 4 formed as afrusto-conical spring or coil of hard temper wire. The copper wire 5 hasa cross-section as shown in FIG. 2 which, as can be seen is generallycircular over part of its circumference but which has two flattenedsurfaces formed by cold rolling or cold drawing which meet the form arelatively sharp ridge 6. This ridge 6 is oriented so that it isdirected toward the interior of the frusto-conical coil 4 and forms ascrew thread. One end 7 of the wire is located at the smaller diameterof the connecting element 4 is bent so that it extends across the axisof the coil and prevents over insertion of the conductor bundle. In someinstances it may be advantageous to expand the diameter of the coil 4 byopening out the ends of the copper wire 5 and retaining them in theirnew position, for example by means of a lip on the solder ring.

A strip 8 of composite solder composition which has been formed into aring and swaged into a frusto-conical shape sits in contact with theouter surface of the coil 4. The composite solder strip is formed from amajor quantity of Sn₆₀ Pb₄₀ non-eutectic composition and has a smalltemperature control ring 9 of pure tin on its outwardly directedsurface.

The device is closed at one end by means of a spherical plug 10 ofsealing material, e.g. irradiated or non-irradiated polyethylene, forexample as described in British Patent Application No. 9002093.4.

The sleeve 3 also contains a moulded ring 11 formed from crosslinkednylon which is positioned between the connecting element 4 and the openend 12 of the sleeve. The internal surface of the ring 11 has a numberof elongate teeth 13 which are oriented at the same angle to the axis ofthe device as the wire 5 in the coil 4.

In operation, during the manufacture of a harness, a number of insulatedwires 2 having their insulation stripped from the ends of the wires, arebundled together and are inserted into the device 1. Complete insertionis achieved by rotating the bundle (in fact, rotating the device aboutthe bundle) so that the end of the conductors are screwed into theconnecting element 4 and the teeth 13 on the ring 11 grip the insulationof the wires and resist them being pulled out of the sleeve 3. At thisstage a dependable low resistance joint has been formed, and the harnessmay be tested by passing electrical signals along the wires 2 andanalysing the results by means of an appropriate microcomputer. Oncethis has been performed, a permanent connection may be formed betweenthe wires 2 simply by heating the sleeve 3, for example by means of aninfrared lamp, a hot-air gun or a small oven, so that it recovers aboutthe bundle of wires 2. During recovery the solder 8 melts and flowsthrough the windings of the coil 4 thereby forming a strong solder jointbetween the conductors of the wires 2 and the connecting element 4. Atthe same time the nylon ring softens and the teeth 13 collapse, therebyallowing the ring 11 to be forced into conformity with the bundle underthe recovery forces of the sleeve 2. Heating is continued until thetemperature control ring 9 of the solder strip has melted, therebyallowing the overlying part of the sleeve 3 to recover fully. Thecompleted joint is shown in FIG. 4 without the solder, for the sake ofclarity.

A second form of device 1 is shown in FIG. 5. This form of device isgenerally similar to the device shown in FIG. 1 but with two exceptions.First, the moulded polyamide ring 11 of FIG. 1 has been replaced with alow recovery temperature polyamide ring that has been formed byextruding a tube and chopping it into short lengths. Secondly, thesolder ring 8 of FIG. 1 has been replaced with a solder ring 8 which islocated adjacent to the larger diameter end of the coil 4. If desiredthe internal surface of the ring 11 may be coated with a layer ofadhesive, preferably a hot-melt adhesive (not shown) in order to providea seal against moisture ingress to the device. In addition oralternatively, one or more thermoplastic sealing rings may be providedin the region of the end 12 of the sleeve 3.

The wire bundle is inserted into the device as described with respect toFIG. 1. When the device is heated in order to recover the sleeve 3, thering 11 will usually recovery slightly before the sleeve 3 and therebyhelp to maintain the wires in position.

FIG. 6 shows a device having two open ends which is suitable for forminga splice between a pair of bundles of conductors. The device comprises adimensionally recoverable sleeve 3 formed from crosslinked and expandedpolyvinylidine fluoride, and a connecting element 16 formed from hardtemper copper wire. The connecting element 16 is formed having twoopposite halves 17 and 18 each of which has a tapering internal surfacefor receiving a separate conductor bundle. As shown, the connectingelement 16 has been formed by wrapping a single piece of wire in thesame sense along its entire length so that the internal surface of bothhalves 17 and 18 both have a right-handed thread. Although the wireforming the connecting element is shown as a circular wire that has beenrolled to form two fiat surfaces and an edge between them, it may bepreferred to employ wire having a square cross-section.

The device is substantially symmetrical about the centre of theconnecting element 16, each half of the device having the same generalconfiguration as that of the device shown in FIG. 5, in which a solderring 8 located adjacent to each end of the connecting element 16. Thedevice has a pair of rings 11 which are constructed, and function,exactly as those shown in FIG. 5.

In operation, in order to form a splice, a bundle of conductors isintroduced into one open end of the device and into one end of theconnecting element 16, and the device is then twisted about the bundleto secure it. The second bundle is then inserted into the other open endof the device and connecting element. After securing the bundle in theconnecting element 16 by twisting, the electrical performance of theharness bundle can be tested and the device then be heated to recoverthe sleeve 3 and form a permanent solder connection.

FIG. 7 shows a further form of device that is suitable for forming anin-line splice between a pair of bundles of conductors. A connectingelement comprises a pair of generally frusto conical coiled parts 20 and21 which are formed from hard tempered copper wire. The wire has asquare cross-section and the edges of the wire form an internal threadin each coiled part, one coiled part 21 having a right handed thread andthe other coiled part 20 having a left handed thread. One of the coiledparts 20 is screwed into the end of a hub element 22 that has aninternal thread, and the other coiled part 21 is mounted over a boss 23of the hub element so that it is freely rotatable.

A ring of solder 24,25 is located about the external surface of eachcoiled part 20 and 21, and a heat-shrinkable polyvinylidine fluoridesleeve 26 and 27 is partially recovered about the coiled parts, solderand a pair of fusible inserts 28 and 29. The lengths and position of thesleeves 26 and 27 is such that they axially overlap for an extent, and afusible ring 30 formed for example from polyethylene is located withinthe end region of sleeve 27 within the region of overlap.

In operation, after a bundle of conductors has been introduced intosleeve 26 and secured in the coiled part 20 of the connecting element, asecond bundle can be inserted into the sleeve 27 and secured within thecoiled part 21 by twisting the sleeve and coiled part about theconductors. This twisting action does not affect the sleeve 26 and thecoiled part 20 and so there is no liklihood of them being unscrewed fromthe bundle.

The splice may then be tested electrically as described above and apermanent joint be formed.

FIGS. 8 and 9 show two alternative forms of connecting element that maybe employed in the device shown in FIG. 7. In the element shown in FIG.8 the ends of the coiled parts 20 and 21 are splayed outwardly to form awaist, and a ting 32 having inwardly bent lateral edges is positionedover the ends of the coiled parts to retain them together while allowingthem to rotate. In FIG. 9 both coiled parts 20 and 21 are fitted over apair of mating collars 33 and 34, one which has a shaft 35 that extendsthrough a hole 36 in the other end is retained therein in such a waythat it can rotate.

I claim:
 1. A device for forming an electrical connection at the end ofa bundle of elongate electrical conductors, which comprises anelectrically insulating sleeve, a metallic connecting element locatedwithin the sleeve, and a quantity of solder located within the sleeveand arranged to form a permanent electrical connection between theconductors, the connecting element having a tapering internal surfacewhich has a screw thread, so that a temporary electrical connection canbe formed by screwing the bundle of conductors into the connectingelement.
 2. A device as claimed in claim 1, wherein the sleeve isdimensionally heat-recoverable.
 3. A device as claimed in claim 1, whichincludes a holding element for resisting withdrawal of the bundle fromthe sleeve before or while the permanent electrical connection isformed.
 4. A device as claimed in claim 3, wherein the holding elementcomprises a ring that is provided with one or more teeth or grippingedges for engaging insulation on the conductors.
 5. A device as claimedin claim 4, wherein the or each tooth or gripping edge has an axialinclination that is substantially the same as the axial inclination ofthe screw thread.
 6. A device as claimed in claim 1, wherein theconnecting element is formed from a tapering coil of wire.
 7. A deviceas claimed in claim 6, wherein the coil is retained in a radiallyexpanded state so that it will radially contract, or attempt radially tocontract when the permanent connection is formed.
 8. A device as claimedin claim 6, wherein the wire has a relatively sharp ridge along itslength which is directed toward the interior of the coil in order toform the screw thread.
 9. A device as claimed in claim 1, wherein theconnecting element is formed from copper.
 10. A device as claimed inclaim 1, wherein the solder is formed from a plurality of compositionsthat have differing melting points.
 11. A device as claimed in claim 1,wherein the solder is in the form of a ring located around theconnecting element.
 12. A device as claimed in claim 11, wherein thesolder element is frusto-conical in shape and sits in contact with theconnecting element.
 13. A device as claimed in claim 2, wherein thesolder is in the form of a ring located around the connecting element.14. A device as claimed in claim 13, wherein the solder element isfrustoconical in shape and sits in contact with the connecting element.15. A device for forming a splice between a pair of bundles of elongateelectrical conductors, which comprises an electrically insulatingsleeve, a metallic connecting element located within the sleeve and aquantity of solder located within the sleeve and arranged to form apermanent electrical connection between the conductors of the bundles,the connecting element having two end portions each of which has atapering internal surface and at least one of which has a screw threadso that a temporary electrical connection can be formed by inserting oneof the bundles of conductors into each end portion of the connectingelement.
 16. A method of forming an electrical harness from a pluralityof insulated electrical wires, which includes:(a) gathering a number ofinsulated wires together to form a bundle at least at the end of thewires; (b) providing a device which comprises an electrically insulatingsleeve, a metallic connecting element located within the sleeve, and aquantity of solder located within the sleeve and arranged to form apermanent electrical connection between the conductors, the connectingelement having a tapering internal surface which has a screw thread; (c)inserting the bundle into the device by means of a screwing action inorder to form a temporary electrical connection; (d) applying electricalsignals to the harness so formed in order to ascertain information aboutit; and (e) heating the sleeve to form a permanent solder connectionbetween the wires.